Microelectronics brought an information revolution through integrating an incredible number of microscopic transistors on single chips. Since this first revolution, huge progresses have been made through the miniaturization and integration of mechanical and/or optical functions in addition to electrical ones. These products are now generally called MEMS or MOEMS (Micro-Opto-Electro-Mechanical-Systems). Accelerometers, inject printer heads, micro-mirrors, micro-relays, pressure sensors are the most known and widespread MEMS. Such products are fabricated using microfabrication processes based on successive and well mastered steps such as thin film deposition, patterning and etching of wafers. Nevertheless, a new generation of MEMS is definitely moving toward highly integrated, more complex and increasingly miniaturized products.
Due to the short life cycle of most new and high-tech products, they have to be produced in smaller and customized batches. Even though microfabrication technology has shown impressive progress during the last decade, where processes are much better known and lots of new materials have been introduced, many limitations remain and are extremely difficult to overcome, especially concerning processes and materials incompatibilities. For those two reasons, micro-assembly, i.e. the 3D integration of hybrid M(O)EMS components (from few µm to few hundreds of µm in size) together, is a natural and powerful approach to overcome those processes incompatibilities and to facilitate complex, heterogeneous, 3D, or out of plane integration. By using basic micro components, micro-assembly thus constitutes a new alternative of MEMS production that may lead to cost saving and shorter development cycle times.
Previous developments enabled lots of proof of concepts (actuators, sensors, gripping principles and tools, control, manipulation…). However, micro-assemblies performed automatically and/or with acceptable yields are, at the same time, extremely recent and challenging topics. It notably requires to simultaneously consider microfabrication tolerances (M(O)EMS components to assemble, handling tools…), robots uncertainties, sensors integration, reliable control, bonding and metrology aspects, where all of these aspects are specific at the microscale (lack of sensors and adapted gripping tools, small signal to noise ratio, use of non linear actuators, surface force predominance…).
